Lithographic printing is based on the principle that oil and water do not mix. A lithographic printing plate has non-image areas which absorb water (hydrophilic areas) and image areas which repel water (hydrophobic areas). For a wet offset lithographic printing, ink is applied to the printing plate to form the image. The plate is dampened so that the ink, which is inherently oily, is rejected by the wet areas and adheres to the image areas. The ink from the inked printing plate is then transferred or “offset” to a rubber blanket. Next, the image on the blanket is transferred to the substrate to produce the printed product.
The standard process of imaging a lithographic printing plate for wet offset printing usually involves use of unhealthy chemicals and using expensive imaging devices, such as computer-to-plate (CTP) devices. In some cases, analog printing devices may be used for imaging. Analog printing employs the use of films and requires chemical processing.
Another process of imaging the lithographic plate is direct imaging, for example using inkjet printers. Currently, the process of imaging an aluminum based lithographic printing plate with inkjet printers requires inkjet printers and inks that are specifically designed for this use. The inks are usually solvent-based or wax-based. Such inks are considerably more expensive and are harmful to the environment.
Therefore, there is a need for a printing member that can be imaged on demand at the print shop in a simple chemistry-free process using non-expensive imaging engines, for example inkjet printers, with water based inks that are environmentally friendly.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.